Method for recycling lithium from waste lithium iron phosphate battery

Abstract

The invention discloses a method for recycling lithium from a waste lithium iron phosphate battery, and belongs to the technical field of waste battery material resource recycling. The method comprises the following steps: carrying out oxidizing roasting on the waste lithium iron phosphate positive electrode material and an iron-based sulfide in an oxygen-containing atmosphere to obtain a roasted material; leaching the roasted material to extract lithium, and carrying out solid-liquid separation to obtain a separated liquid and lithium extraction slag; the separation liquid is subjected to precipitation iron removal and solid-liquid separation, and lithium-rich liquid containing bicarbonate radical ions and ferric hydroxide precipitation are obtained; and reacting the lithium-rich liquid with an alkaline substance under a heating condition to obtain lithium carbonate. The method has the advantages of high selectivity, less impurity introduction, simple process flow and the like, can realize efficient recovery and resource utilization of lithium, and promotes the lithium battery recovery industry to develop towards a clean, efficient and sustainable direction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of recycling and utilization of waste battery materials, in particular to a method for recovering lithium from waste lithium iron phosphate batteries. BACKGROUND

[0002] With the rapid development of electric vehicles and energy storage systems, lithium iron phosphate batteries are widely used due to their safety and long cycle life, which leads to the disposal and resource utilization of a large number of retired batteries. At present, the recovery of waste lithium iron phosphate batteries mainly adopts the process route of pyroprocessing pretreatment combined with hydrometallurgical leaching. Since lithium iron phosphate material has a stable olivine crystal structure, lithium ions are firmly bound in the crystal lattice, so the direct leaching efficiency is very low, and therefore the structure needs to be destroyed by roasting to convert lithium into a soluble form.

[0003] In the existing roasting process, alkali metal or alkaline earth metal salts such as sodium salt, potassium salt, calcium salt, and magnesium salt are often used as additives to convert lithium into lithium sulfate by using the sulfur oxides released by the decomposition of the additives at high temperatures. However, such traditional additives inevitably introduce a large amount of non-lithium metal ions during the reaction process, significantly increasing the purification burden of the mother liquor in the subsequent wet lithium extraction process, which not only complicates the process and increases the cost, but also easily affects the product purity of the final lithium carbonate. In addition, a large amount of phosphorus-iron slag with a composition of Fe-P-O is produced after extracting lithium, and the slag has a complex composition, high impurity content, and unstable phase.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The present application aims to provide a method for recovering lithium from waste lithium iron phosphate batteries to solve or improve the above technical problems.

[0006] The present application can be achieved as follows: In a first aspect, the present application provides a method for recovering lithium from waste lithium iron phosphate batteries, comprising the following steps: oxidizing roasting waste lithium iron phosphate cathode material with iron-based sulfide in an oxygen-containing atmosphere to obtain roasted material; leaching lithium from the roasted material, solid-liquid separation to obtain a separation liquid and a lithium extraction residue; precipitating and removing iron from the separation liquid, solid-liquid separation to obtain a lithium-rich liquid containing bicarbonate ions and a ferric hydroxide precipitate; and reacting the lithium-rich liquid with an alkaline substance under heating conditions to obtain lithium carbonate.

[0007] In an optional embodiment, the molar ratio of Li element in the waste lithium iron phosphate cathode material to S element in the iron-based sulfide is 1:1 to 1:2.

[0008] In an optional embodiment, the iron-based sulfide includes at least one of ferrous sulfide and ferrous sulfide.

[0009] In an optional embodiment, waste lithium iron phosphate cathode material and iron-based sulfide are first ball-milled under a protective atmosphere to obtain ball milling material; then the ball milling material is oxidized and roasted under an oxygen-containing atmosphere to obtain roasted material.

[0010] In an optional embodiment, the oxidative calcination temperature is 650℃~800℃, and the oxidative calcination time is 1h~3h.

[0011] In an optional embodiment, the leaching temperature for lithium extraction is 50°C to 70°C, and the leaching time is 0.5h to 2h.

[0012] In an optional embodiment, the ratio of leaching reagent to calcined material used for lithium extraction is (5mL~10mL):1g.

[0013] In an optional embodiment, the leaching agent includes at least one of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, and water.

[0014] In an optional embodiment, the step of precipitating iron from the separation liquid includes: mixing the separation liquid with an oxidant to obtain a mixed solution; mixing the mixed solution with an ammonia-ammonium bicarbonate buffer solution and aging it.

[0015] In an optional embodiment, the oxidant is used to remove Fe from the separation liquid. 2+ Completely oxidized to Fe 3+ .

[0016] In an optional implementation, the oxidant includes hydrogen peroxide.

[0017] In an optional embodiment, the pH of the system after mixing the mixed solution with the ammonia-ammonium bicarbonate buffer solution is 6.5~7.5; And / or, the molar amount of carbonate in the ammonia-ammonium bicarbonate buffer solution is 0.7 to 0.8 times the molar amount of Li in the mixed solution.

[0018] In an optional embodiment, the pH value of the system after mixing the lithium-rich solution with the alkaline substance is 11-12; And / or, the heating temperature is 90℃~105℃; And / or, heat and evaporate to concentrate to 20%~25% of the original volume of the lithium-rich liquid.

[0019] The beneficial effects of this invention include: The method provided by this invention introduces iron-based sulfides as roasting aids, which undergo an oxidation reaction during oxidative roasting to generate SO3. SO3 gas acts as a strong acidifier, disrupting the olivine structure of lithium iron phosphate, promoting lithium ion deintercalation and intercalation, and binding with sulfate ions. This selectively converts lithium ions into easily leached sulfates, enabling efficient lithium leaching even under low acid concentrations or water leaching conditions. After leaching, iron is removed by precipitation to obtain a lithium-rich solution containing bicarbonate ions. This lithium-rich solution can generate lithium carbonate under alkaline conditions and heating, thus achieving efficient one-step precipitation of lithium-containing solutions. The above method features a short process flow, low energy consumption, simple operation, ease of industrialization, low impurities, and the production of high-purity lithium carbonate products. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A process flow diagram of the method for recovering lithium from spent lithium iron phosphate batteries provided by the present invention; Figure 2 The image shows the XRD pattern of the calcined material in Example 1. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] The method for recovering lithium from spent lithium iron phosphate batteries provided by this invention will be described in detail below.

[0024] This invention provides a method for recovering lithium from spent lithium iron phosphate batteries, such as... Figure 1 As shown, the following steps may be included: S1: Waste lithium iron phosphate cathode material and iron-based sulfides are oxidized and roasted in an oxygen-containing atmosphere to obtain roasted material.

[0025] In some alternative embodiments, waste lithium iron phosphate cathode material is first ball-milled with iron-based sulfides under a protective atmosphere to obtain ball milling material; then the ball milling material is oxidized and calcined under an oxygen-containing atmosphere to obtain calcined material.

[0026] The above-mentioned ball milling process can be carried out in a planetary ball mill. Through ball milling, the waste lithium iron phosphate cathode material and iron-based sulfides are fully and uniformly mixed.

[0027] In some alternative embodiments, the molar ratio of Li to S in the waste lithium iron phosphate cathode material can be from 1:1 to 1:2, such as 1:1, 1:1.5, or 1:2, or other values ​​within the range of 1:1 to 1:2. For example, the iron-based sulfide may include at least one of ferrous disulfide and ferrous sulfide.

[0028] In this invention, the aforementioned iron-based sulfides serve as calcination aids to generate SO3 and disrupt the olivine structure of lithium iron phosphate during oxidative calcination, thereby improving the efficiency of Li- leaching in subsequent processes. + The leaching rate is affected by several factors. If the molar ratio of Li to S in the iron-based sulfide in the waste lithium iron phosphate cathode material is inappropriate (e.g., 1:2), the excessive sulfur source (iron-based sulfide) will lead to the formation of a large amount of soluble ferric sulfate or ferrous sulfate impurities in the reaction system, resulting in a significant increase in the iron ion concentration in the leachate, which is detrimental to subsequent impurity removal processes. If the molar ratio of Li to S in the iron-based sulfide in the waste lithium iron phosphate cathode material is inappropriate (e.g., 1:0.5), the stoichiometric ratio of the sulfur source (iron-based sulfide) participating in the reaction is insufficient, and it is impossible to provide enough SO3 gas to completely destroy the lithium iron phosphate crystal structure, which is detrimental to lithium ion leaching.

[0029] In some alternative embodiments, the oxidative calcination temperature can be 650℃~800℃, such as 650℃, 680℃, 700℃, 720℃, 750℃, 780℃ or 800℃, or other values ​​within the range of 650℃~800℃.

[0030] If the oxidative roasting temperature is below 600℃, the reaction kinetics are insufficient, which is not conducive to the oxidation reaction of iron-based sulfides; if the oxidative roasting temperature is above 800℃, sintering will occur, causing the material to clump together, which is not conducive to the full progress of the reaction.

[0031] The oxidative calcination time can be 1h to 3h, such as 1h, 1.5h, 2h, 2.5h or 3h, or other values ​​within the range of 1h to 3h.

[0032] The preferred oxygen atmosphere is an oxygen atmosphere.

[0033] During the above-mentioned oxidative roasting process, iron-based sulfides undergo an oxidation reaction to generate SO3. SO3 gas acts as a strong acidifying agent, attacking the unstable lithium-containing mesophase, promoting the deintercalation of lithium ions and their combination with sulfate ions to transform into water-soluble lithium sulfate. Meanwhile, iron is oxidized to Fe2O3, mainly through the following reactions: ; ; ; ; .

[0034] Therefore, by using iron sulfide compounds as calcination aids and utilizing their oxidation reaction to generate SO3, the olivine structure of lithium iron phosphate can be efficiently destroyed, enabling lithium leaching to be achieved even under low acid concentrations or even water immersion conditions.

[0035] S2: Leach lithium from the roasted material, separate the solid and liquid phases to obtain the separated liquid and lithium extraction residue.

[0036] In some alternative embodiments, the leaching temperature for lithium extraction can be 50°C to 70°C, such as 50°C, 55°C, 60°C, 65°C, or 70°C, or other values ​​within the range of 50°C to 70°C.

[0037] The leaching time for lithium extraction can be 0.5h to 2h, such as 0.5h, 1h, 1.5h or 2h, or other values ​​within the range of 0.5h to 2h.

[0038] In some optional embodiments, the ratio of leaching reagent to roasted material used for lithium extraction can be (5mL~10mL):1g, such as 5mL:1g, 6mL:1g, 7mL:1g, 8mL:1g, 9mL:1g or 10mL:1g, or other values ​​within the range of (5mL~10mL):1g.

[0039] In some optional embodiments, the leaching agent may exemplary include at least one of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, and water, preferably at least one of dilute sulfuric acid, dilute hydrochloric acid, and dilute nitric acid, wherein the acidic agent has a H+ content. + The concentration can, for example, not exceed 1 mol / L.

[0040] The lithium extraction slag mentioned above is mainly Fe2O3. This lithium extraction slag can be recycled as an iron-phosphorus source raw material for iron oxide red pigment or iron phosphate precursor.

[0041] S3: The separation liquid is subjected to precipitation to remove iron, and solid-liquid separation is performed to obtain a lithium-rich liquid containing bicarbonate ions and iron hydroxide precipitate.

[0042] In some alternative embodiments, the step of precipitating iron from the separation liquid may include: mixing the separation liquid with an oxidant to obtain a mixed solution; mixing the mixed solution with an ammonia-ammonium bicarbonate buffer solution and aging it.

[0043] For example, add an appropriate amount of hydrogen peroxide as an oxidant to the separation solution and stir continuously (e.g., for 30 minutes) to ensure that the Fe in the separation solution is separated. 2+ Completely oxidized to Fe 3+ The oxidizing agent may, exemplarily, include hydrogen peroxide. Due to Fe... 2+ The pH value of the completely hydrolyzed precipitate is greater than that of Fe. 3+ The pH value at which complete hydrolysis and precipitation occur, therefore, Fe is oxidized by an oxidant. 2+ Oxidized to Fe 3+ This can significantly reduce the precipitation of Fe in the following steps. 3+ The required amount of alkaline substance.

[0044] In some optional embodiments, the pH of the system after mixing the mixed solution with the ammonia-ammonium bicarbonate buffer solution can be 6.5~7.5, such as 6.5, 6.8, 7.0, 7.2 or 7.5, or other values ​​within the range of 6.5~7.5. The OH- ions in the system within the above pH range... - The concentration was much higher than that of Fe. 3+ The concentration required for complete precipitation, therefore, can make Fe 3+ Hydrolysis produces ferric hydroxide precipitate. Furthermore, it should be noted that, in situations where Fe... 3+ Within the pH range for complete precipitation, this invention further controls the pH value within a neutral to slightly alkaline range of 6.5 to 7.5, enabling HCO3 to undergo precipitation. - The pH value should be kept stable to facilitate subsequent lithium precipitation. If the pH value is controlled in a slightly acidic range (such as 4.5~5.5), bicarbonate ions and hydrogen ions will combine to form carbon dioxide, which is not conducive to subsequent lithium precipitation.

[0045] In some optional embodiments, the molar amount of carbonate in the ammonia-ammonium bicarbonate buffer solution can be 0.7 to 0.8 times the molar amount of Li in the mixed solution, such as 0.7, 0.75, or 0.8 times, or other values ​​within the range of 0.7 to 0.8 times. Within this range, bicarbonate is in excess in the system, and the excess carbonate ions can be converted to carbonate ions in step S4, reacting with Li... + It further generates lithium carbonate.

[0046] Compared to existing methods that use sodium hydroxide precipitation to remove iron, this invention uses an ammonia-ammonium bicarbonate buffer system to regulate the pH value, avoiding local over-alkaliness. This allows impurities to precipitate in the form of coarse crystals that are easy to filter and wash, preventing the formation of Fe(OH)3 colloids and reducing the loss of lithium ions caused by chemical co-precipitation and physical entrainment.

[0047] S4: Lithium carbonate is obtained by reacting lithium-rich liquid with an alkaline substance under heating conditions.

[0048] In some alternative implementations, the pH value of the system after mixing the lithium-rich solution with the alkaline substance can be 11 to 12, such as 11, 11.5 or 12, or other values ​​in the range of 11 to 12.

[0049] The alkaline substance can be, for example, a sodium hydroxide solution. NaOH solution is added to the lithium-rich solution to adjust the pH of the mixture to 11-12, thereby converting bicarbonate ions into carbonate ions.

[0050] In some alternative embodiments, the heating temperature can be 90°C to 105°C, such as 90°C, 95°C, 100°C or 105°C, or other values ​​within the range of 90°C to 105°C.

[0051] In some alternative embodiments, the lithium-rich liquid is concentrated by heating and evaporation to 20% to 25% of its original volume, such as 20%, 22%, or 25%, or other values ​​within the range of 20% to 25%. This can also be understood as heating and evaporating to concentrate 75% to 80% of the original volume of the lithium-rich liquid.

[0052] After evaporation and concentration, the product is filtered while hot, washed and dried to obtain lithium carbonate.

[0053] By quantitatively introducing ammonium bicarbonate in the impurity removal stage in step S3, and then adding alkali and heating during the evaporation and concentration process in step S4, the bicarbonate ions are converted into carbonate ions, directly precipitating lithium carbonate. This method eliminates the need for additional precipitants such as sodium carbonate, significantly simplifying the operation steps. The entire process is concise, compact, and easy to operate.

[0054] Building upon the above, the method provided by this invention features a short process flow, low energy consumption, simple operation, and ease of industrialization. By introducing iron-based sulfides as calcination aids, the SO3 generated from their oxidation reaction efficiently disrupts the crystal structure of lithium iron phosphate, selectively converting lithium into easily leached sulfates. Through an ammonia-ammonium bicarbonate buffer system, deep purification of iron ions is achieved while minimizing lithium ion entrainment and chemical co-precipitation losses. Simultaneously, through precise design of the stoichiometry, the buffer introduced during the impurity removal stage provides the necessary carbonate ions for subsequent lithium precipitation, thereby achieving efficient one-step precipitation of lithium-containing solutions.

[0055] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0056] Example 1 This embodiment provides a method for recovering lithium from spent lithium iron phosphate batteries, including the following steps: S1: 100g of waste lithium iron phosphate cathode material powder and 83.58g of iron-based sulfide (FeS) were ball-milled in a nitrogen atmosphere using a planetary ball mill to obtain ball-milled material. The ball-milled material was placed in a muffle furnace, oxygen was introduced, and the temperature was raised to 700℃ at a rate of 5℃ / min for oxidative calcination for 2 hours to obtain calcined material.

[0057] The molar ratio of Li to S in the waste lithium iron phosphate cathode material powder is 1:1.75. The XRD pattern of the above-mentioned calcined material is shown below. Figure 2 As shown, Figure 2 The presence of significant Li2SO4 characteristic diffraction peaks indicates that the crystal structure of the raw material lithium iron phosphate has been destroyed, and lithium ions have undergone sulfation reaction, transforming into the water-soluble lithium sulfate phase. Along with the extraction of lithium, iron elements are mainly transformed into Fe2O3.

[0058] S2: The roasted material is mixed with dilute sulfuric acid with a concentration of 1 mol / L at a solid-liquid ratio of 1 g: 8 mL and stirred at 70 °C for 1 h to leach lithium. Then, solid-liquid separation is performed by vacuum extraction to obtain the separated liquid and lithium extraction residue.

[0059] S3: Add an appropriate amount of hydrogen peroxide to the separation solution and stir continuously for 30 minutes to ensure that the Fe in the separation solution is removed. 2+ Completely oxidized to Fe 3+ A mixed solution was obtained. Ammonium bicarbonate solid was weighed and dissolved in concentrated ammonia water to prepare an ammonia-ammonium bicarbonate buffer solution, with the molar amount of carbonate in the ammonia-ammonium bicarbonate buffer solution being 0.75 times the molar amount of Li in the mixed solution. The ammonia-ammonium bicarbonate buffer solution was then slowly added dropwise to the mixed solution to adjust the pH to 6.5. After aging for 1 hour, solid-liquid separation was performed by filtration to obtain a lithium-rich solution containing bicarbonate ions and an iron hydroxide precipitate.

[0060] S4: Add NaOH solution directly to the lithium-rich solution containing bicarbonate ions to adjust the pH value to 12, then heat to 100℃ for evaporation and concentration. When the volume of the lithium-rich solution is reduced to 20% of its original volume, stop heating and filter while hot. Wash the filter cake three times with hot water and dry at 100℃ to obtain the Li2CO3 product.

[0061] Example 2 This embodiment provides a method for recovering lithium from spent lithium iron phosphate batteries, including the following steps: S1: 100g of waste lithium iron phosphate cathode material powder and 95.44g of iron-based sulfide (FeS) were ball-milled in a nitrogen atmosphere using a planetary ball mill to obtain ball-milled material. The ball-milled material was placed in a muffle furnace, oxygen was introduced, and the temperature was raised to 800℃ at a rate of 5℃ / min for oxidative calcination for 1 hour to obtain calcined material.

[0062] The molar ratio of Li to S in waste lithium iron phosphate cathode material powder is 1:2.

[0063] S2: The roasted material and deionized water are mixed at a solid-liquid ratio of 1g:10mL and stirred at 60℃ for 0.5h to leach lithium. Then, solid-liquid separation is performed by vacuum extraction to obtain the separated liquid and lithium extraction residue.

[0064] S3: Add an appropriate amount of hydrogen peroxide to the separation solution and stir continuously for 30 minutes to ensure that the Fe in the separation solution is removed. 2+ Completely oxidized to Fe 3+ A mixed solution was obtained. Ammonium bicarbonate solid was weighed and dissolved in concentrated ammonia water to prepare an ammonia-ammonium bicarbonate buffer solution, with the molar amount of carbonate in the ammonia-ammonium bicarbonate buffer solution being 0.8 times the molar amount of Li in the mixed solution. The ammonia-ammonium bicarbonate buffer solution was then slowly added dropwise to the mixed solution to adjust the pH to 7. After aging for 1 hour, solid-liquid separation was performed by filtration to obtain a lithium-rich solution containing bicarbonate ions and an iron hydroxide precipitate.

[0065] S4: Add NaOH solution directly to the lithium-rich solution containing bicarbonate ions to adjust the pH value to 11, then heat to 90℃ for evaporation and concentration. When the volume of the lithium-rich solution is reduced to 25% of the original volume, stop heating and filter while hot. Wash the filter cake three times with hot water and dry at 100℃ to obtain the Li2CO3 product.

[0066] Example 3 This embodiment provides a method for recovering lithium from spent lithium iron phosphate batteries, including the following steps: S1: 100g of waste lithium iron phosphate cathode material powder and 32.53g of iron-based sulfide (pyrite with a FeS2 content of 90wt%) were ball-milled in a planetary ball mill under a nitrogen atmosphere to obtain ball-milled material. The ball-milled material was placed in a muffle furnace, oxygen was introduced, and the temperature was raised to 650℃ at a rate of 5℃ / min for oxidative roasting for 3 hours to obtain roasted material.

[0067] The molar ratio of Li to S in waste lithium iron phosphate cathode material powder is 1:1.

[0068] S2: The roasted material is mixed with dilute sulfuric acid with a concentration of 1 mol / L at a solid-liquid ratio of 1 g: 5 mL and stirred at 50 °C for 2 h to leach lithium. Then, solid-liquid separation is performed by vacuum extraction to obtain the separated liquid and lithium extraction residue.

[0069] S3: Add an appropriate amount of hydrogen peroxide to the separation solution and stir continuously for 30 minutes to ensure that the Fe in the separation solution is removed. 2+ Completely oxidized to Fe3+ A mixed solution was obtained. Ammonium bicarbonate solid was weighed and dissolved in concentrated ammonia water to prepare an ammonia-ammonium bicarbonate buffer solution, with the molar amount of carbonate in the ammonia-ammonium bicarbonate buffer solution being 0.7 times the molar amount of Li in the mixed solution. The ammonia-ammonium bicarbonate buffer solution was then slowly added dropwise to the mixed solution to adjust the pH to 7.5. After aging for 1 hour, solid-liquid separation was performed by filtration to obtain a lithium-rich solution containing bicarbonate ions and an iron hydroxide precipitate.

[0070] S4: Add NaOH solution directly to the lithium-rich solution containing bicarbonate ions to adjust the pH value to 11.8, then heat to 105℃ for evaporation and concentration. When the volume of the lithium-rich solution is reduced to 22% of the original volume, stop heating and filter while hot. Wash the filter cake three times with hot water and dry at 100℃ to obtain the Li2CO3 product.

[0071] Comparative Example 1 The difference between this comparative example and Example 1 is that in step S1, only the waste lithium iron phosphate cathode material is ball-milled under a protective atmosphere. That is, this comparative example does not use iron-based sulfides as calcination aids.

[0072] Comparative Example 2 The difference between this comparative example and Example 1 is that in S1, the molar ratio of Li element in the waste lithium iron phosphate cathode material to S element in the iron-based sulfide is 1:0.5.

[0073] Comparative Example 3 The difference between this comparative example and Example 1 is that in S3, the pH value of the system after mixing the mixed solution with ammonia-ammonium bicarbonate buffer is 9.0.

[0074] Test case The leaching rates of lithium and iron, the recovery rate of lithium, the precipitation rate of iron ions, and the purity of lithium carbonate products in Examples 1-3 and Comparative Examples 1-3 were compared, and the results are shown in Table 1.

[0075] Table 1 Test Results

[0076] As can be seen from Table 1, the method provided by the embodiments of the present invention can selectively and effectively leach lithium from waste lithium iron phosphate cathode material powder, and obtain a high lithium leaching rate and lithium recovery rate. At the same time, the method provided by the present invention can also ensure that the small amount of iron ions contained in the separation liquid are completely precipitated and removed, thereby obtaining a high-purity lithium carbonate product.

[0077] As can be seen from Example 1 and Comparative Examples 1-3, improper operation or inadequate condition control can lead to a decrease in lithium leaching rate, recovery rate, or purity of lithium carbonate products.

[0078] In summary, the method provided by this invention features a short process flow, low energy consumption, simple operation, and ease of industrialization. By introducing iron-based sulfides as calcination aids, the SO3 generated from their oxidation reaction efficiently disrupts the crystal structure of lithium iron phosphate, selectively converting lithium into easily leached sulfates. Through an ammonia-ammonium bicarbonate buffer system, deep purification of iron ions is achieved while minimizing lithium ion entrainment and chemical co-precipitation losses. Simultaneously, through precise design of the stoichiometry, the buffer introduced during the impurity removal stage provides the necessary carbonate ions for subsequent lithium precipitation, thus achieving efficient one-step precipitation of lithium-containing solutions.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recovering lithium from spent lithium iron phosphate batteries, characterized in that, Includes the following steps: Waste lithium iron phosphate cathode material and iron-based sulfides are oxidized and roasted in an oxygen-containing atmosphere to obtain roasted material. The roasted material is subjected to leaching for lithium extraction, followed by solid-liquid separation to obtain a separated liquid and lithium extraction residue. The separated liquid is subjected to precipitation to remove iron, and solid-liquid separation is performed to obtain a lithium-rich liquid containing bicarbonate ions and an iron hydroxide precipitate; the lithium-rich liquid is reacted with an alkaline substance under heating conditions to obtain lithium carbonate.

2. The method according to claim 1, characterized in that, The molar ratio of Li to S in the waste lithium iron phosphate cathode material is 1:1 to 1:

2. Preferably, the iron-based sulfide includes at least one of ferrous disulfide and ferrous sulfide.

3. The method according to claim 1, characterized in that, First, the waste lithium iron phosphate cathode material and the iron-based sulfide are ball-milled under a protective atmosphere to obtain ball milling material; then, the ball milling material is oxidized and roasted under an oxygen-containing atmosphere to obtain roasted material.

4. The method according to claim 1, characterized in that, The oxidative roasting temperature is 650℃~800℃, and the oxidative roasting time is 1h~3h.

5. The method according to claim 1, characterized in that, The leaching temperature for lithium extraction is 50℃~70℃, and the leaching time is 0.5h~2h.

6. The method according to claim 1, characterized in that, The ratio of the leaching reagent used for lithium extraction to the calcined material is (5mL~10mL):1g; Preferably, the leaching reagent includes at least one of dilute sulfuric acid, dilute hydrochloric acid, dilute nitric acid, and water.

7. The method according to claim 1, characterized in that, The step of precipitating and removing iron from the separated liquid includes: mixing the separated liquid with an oxidant to obtain a mixed solution; mixing the mixed solution with an ammonia-ammonium bicarbonate buffer solution and aging it.

8. The method according to claim 7, characterized in that, The oxidant is used to remove Fe from the separation liquid. 2+ Completely oxidized to Fe 3+ ; Preferably, the oxidant includes hydrogen peroxide.

9. The method according to claim 7, characterized in that, The pH value of the system after mixing the mixed solution with ammonia-ammonium bicarbonate buffer solution is 6.5~7.5; And / or, the molar amount of carbonate ions contained in the ammonia-ammonium bicarbonate buffer solution is 0.7 to 0.8 times the molar amount of Li element in the mixed solution.

10. The method according to claim 1, characterized in that, The pH value of the system after the lithium-rich solution is mixed with the alkaline substance is 11~12; And / or, the heating temperature is 90℃~105℃; And / or, heat and evaporate to concentrate to 20%~25% of the original volume of the lithium-rich liquid.

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